Arctic melting vs AO

Arctic melting  vs AO

Since there is a small but significant circa 14d pseudo cyclic variation in ice cover around min/max events. This is probably due to changes in magnitude of the dirunal tides that are known to have variations of around 13.5 and 14.5 days. There can also be notable short term changes due to storminess, especially around the summer minimum. It is important to isolate this when attempting to measure the length of freezing and melting periods.

The min/max area dates were estimated by finding the first data after the zero-crossing of the time derivative of Arctic ice area.

Ice cover data was processed using a gaussian-derivative* convolution filter. This provides a more accurate estimation of the derivative function as well a providing the low-pass filtering required to remove the ripple. This was found to be the minimal length that gave stable results.

Longer filters gave very similar results but reduced the year to year variation.

Since melting season only gives one point per year, AO index was filtered with a 365 day filter, then scaled and shifted so that it neutral point was six months (0.5).

* gaussian-derivative with sigma = 13 days
The width of the central peak of the 13d gaussian is similar to that of 26 day running mean “smoother” but with a far superior frequency response.

Data for graph above in first two columns

Third col is annual change in area (unchecked: caveat emptor)

# year melting season (d_area ?)
1979 0.528417 -9.43651
1980 0.501037 -9.05165
1981 0.481872 -9.21597
1982 0.503775 -9.5304
1983 0.509251 -8.93974
1984 0.48461 -9.39725
1985 0.459968 -9.50552
1986 0.501037 -8.87501
1987 0.509251 -9.3121
1988 0.487348 -9.70018
1989 0.564009 -8.73724
1990 0.52294 -9.76096
1991 0.514727 -9.43568
1992 0.511989 -9.31876
1993 0.490086 -10.2413
1994 0.501038 -9.3856
1995 0.539368 -9.34537
1996 0.511989 -8.11779
1997 0.528416 -8.94755
1998 0.525679 -10.2618
1999 0.47092 -9.84008
2000 0.509251 -9.67688
2001 0.487348 -9.54703
2002 0.511989 -9.95161
2003 0.503776 -9.86068
2004 0.509251 -9.13722
2005 0.481872 -9.21381
2006 0.503775 -9.05517
2007 0.522941 -10.2829
2008 0.501037 -10.8469
2009 0.501038 -10.1025
2010 0.479134 -10.5337
2011 0.48461 -9.99179
2012 0.479134 -11.3853

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